Hybrid renewable energy systems (HRES) have been widely identified as an efficient mechanism to generate electrical power based on renewable energy sources (RES). This kind of energy generation systems are based on the combination of one or more RES allowing to complement the weaknesses of one with strengths of another and, therefore, reducing installation costs with an optimized installation. To do so, optimization methodologies are a trendy mechanism because they allow attaining optimal solutions given a certain set of input parameters and variables. This work is focused on the optimal sizing of hybrid grid-connected photovoltaic-wind power systems from real hourly wind and solar irradiation data and electricity demand from a certain location. The proposed methodology is capable of finding the sizing that leads to a minimum life cycle cost of the system while matching the electricity supply with the local demand. In the present article, the methodology is tested by means of a case study in which the actual hourly electricity retail and market prices have been implemented to obtain realistic estimations of life cycle costs and benefits. A sensitivity analysis that allows detecting to which variables the system is more sensitive has also been performed. Results presented show that the model responds well to changes in the input parameters and variables while providing trustworthy sizing solutions. According to these results, a grid-connected HRES consisting of photovoltaic (PV) and wind power technologies would be economically profitable in the studied rural township in the Mediterranean climate region of central Catalonia (Spain), being the system paid off after 18 years of operation out of 25 years of system lifetime. Although the annual costs of the system are notably lower compared with the cost of electricity purchase, which is the current alternative, a significant upfront investment of over $10 M - roughly two thirds of total system lifetime cost - would be required to install such system. (C) 2015 Elsevier Ltd. All rights reserved.Postprint (author's final draft

Hybrid renewable energy systems (HRES) are a trendy alternative to enhance the renewable energy deployment worldwide. They effectively take advantage of scalability and flexibility of these energy sources, since combining two or more allows counteracting the weaknesses of a stochastic renewable energy source with the strengths of another or with the predictability of a non-renewable energy source. This work presents an optimization methodology for minimum life cycle cost of a HRES based on solar photovoltaic, wind and biomass power. Biomass power seeks to take advantage of locally available forest wood biomass in the form of wood chips to provide energy in periods when the PV and wind power generated are not enough to match the existing demand. The results show that a HRES combining the selected three sources of renewable energy could be installed in a rural township of about 1300 dwellings with an up-front investment of US $7.4 million, with a total life cycle cost of slightly more than US $30 million. Such a system would have benefits in terms of energy autonomy and environment quality improvement, as well as in term of job opportunity creation.

This paper proposes a novel and innovative methodology to assess the degree of Circularity in one of the most resource-consuming and impactful economic activities: the building construction and/or renovation works. The proposed approach measures the ratio of circular flows in three aspects: energy, water and materials consumption; and combines them with the measure of social added value and economic value of the entire activity along its life cycle, regardless of being a new building construction or a major renovation work. The whole methodology has been developed under a life cycle perspective, incorporating into the analysis all material flows and social, environmental and economic impacts from cradle to grave, i.e., from resource acquisition to end of life treatment processes or disposal. The proposed Key Performance Indicators (KPIs) measure different and non-directly related parameters (energy, materials, social impact…) and they are both quantitative and qualitative metrics. Hence, the proposed methodology performs the indicators calculation procedure independently. The methodology has been tested with a conventional energy renovation process consisting of an installation of an External Thermal Insulation Composite System (ETICS) – one of the most prevailing façade energy retrofitting alternatives – combined with a rooftop solar PV system. In this way, a calculation example is shown and some lessons can be extracted regarding the degree circularity of current building construction and refurbishment practices. Results show that current building envelope solutions – even including an efficient rooftop PV system – are far from being considered circular: whereas a significant 51% of Energy Circularity is achieved, only a 29% and a 21% degree of Circularity is observed for the materials and social aspects, also with high payback periods – above 20 years – on the economic side. The methodology also succeeds in showing the potential for improvement and its location along the building life cycle. It is also shown that buildings behave significantly different in each of the addressed CE aspects: materials, energy and water use, social added value and life cycle cost; showing also different potential of improvement.